President Barack Obama has lifted US economic sanctions on Myanmar, terminating an emergency order that deemed the policies of the former military government a threat to US national security.

"I have determined that the situation that gave rise to the national emergency with respect to Burma has been significantly altered by Burma's substantial advances to promote democracy, including historic elections in November 2015," Mr Obama said in a letter to the US House and Senate speakers.

He said the US intended to use other means to support Myanmar.

"While Burma faces significant challenges, including the consolidation of its democracy, the United States can, and intends to, use other means to support the government and people of Burma in their efforts to address these challenges," Mr Obama's letter said.

Some members of the US congress have expressed concern about the extent and durability of change in Myanmar and introduced legislation seeking to give politicians some influence on the process of easing sanctions.

Senator Ben Cardin, the top ranking Democrat on the Senate Foreign Relations Committee, voiced support for the sanctions action, but concern over the plight of Rohingya Muslims, ethnic reconciliation and reform of a junta-era constitution that guarantees the military a quarter of parliamentary seats.

"Even as we lift these sanctions, we must maintain a focus on on-going concerns regarding the role of the military in Burma's economy and politics," Senator Cardin said in a statement.